1. Field of the Invention
The present invention relates to an image forming apparatus and a sheet setting control method that can be suitably applied to a copying machine or the like, which has a color mode in which a color image is outputted and a black-and-white mode in which a black-and-white image is outputted.
2. Description of the Related Art
In a conventional image forming apparatus capable of outputting a color image, in the case where a free size sheet is used as a recording medium on which an image is formed, the user has to input the lengths of the free size sheet in the vertical and horizontal directions thereof for the following reasons. If the sheet size is unknown, in the case where the size of an image to be outputted exceeds the sheet size, surplus toner beyond the sheet size scatters in the apparatus to form an unfavorable image or cause failure of the apparatus. In particular, if the mage forming apparatus is a 1D (drum) type image forming apparatus that forms a color image using one photosensitive body, image formation takes more time, and hence the scatter of toner in the apparatus is likely to cause troubles.
A conventional image forming apparatus capable of outputting a black-and-white image also has the problem that toner may scatter for the reasons stated above, but this problem occurs only with a low possibility because the formation of a black-and-white image takes less time as compared with a color image, and the scatter of toner usually has a smaller effect on the image quality of a black-and-white image than on that of a color image. Therefore, the conventional image forming apparatus capable of outputting a black-and-white image usually does not force the user to set the size of a free size sheet. On the other hand, a conventional image forming apparatus capable of outputting both a color image and a black-and-white image requires the user to input the lengths of a sheet in the vertical and horizontal directions even when a black-and-white image is formed on a free size sheet.
The above described prior art, however, has the following problems. Since the image forming apparatus capable of outputting both a color image and a black-and-white image requires the user to input the lengths of a sheet in the vertical and horizontal directions even when a black-and-white image is formed, the necessity of performing a complicated inputting operation imposes a heavy burden on the user who has more opportunities to form a black-and-white image than a color image (for example, Japanese Laid-Open Patent Publication (Kokai) Nos. 2000-159391, 10-126611, 09-068896 and 09-160444).